Turbulence structure of compound open-channel flows with one-line emergent vegetation

摘要

Vegetation such as trees and shrubs are often observed at the floodplain edge in natural rivers. Spanwise profiles of streamwise velocity component are influenced significantly by the drag force of trees. That is to say, the streamwise velocity decreases locally behind trees and near the junction between the main-channel and the floodplain.This property is quite different from that observed in typical compound open-channel flows, in which the velocity profile has a single inflection point and forms a mixing layer related to large-scale horizontal vortices. In contrast, in compound openchannel flow with a one-line emergent vegetation, a “V“- shaped velocity profile appears with twin inflection points. It is thus very important to investigate these hydrodynamic properties and turbulence structure considering the emergent vegetation effects in river engineering and eco hydraulics. So, in the present study, turbulence measurements by 3-D acoustic Doppler anemometer (ADV) were conducted in 150cm wide laboratory flume, in which 2cm diameter and 25cm height cylinders are placed as vegetation models with 10cm span along the junction edge.